1. Field of the Invention
This invention relates to a process for the formation of a neutralized sulfonated polymer having about 10 to about 60 meq. sulfonate groups, wherein the sulfonate groups are neutralized with a barium counterion. A cement of a polymer having olefinic functional groups and a non-reactive solvent is contacted with a sulfonating agent such as an acyl sulfate. After terminating the sulfonation reaction by quenching with methanol, the sulfonated polymer is then neutralized with a solution of barium hydroxide, barium acetate or barium carboxylate dissolved in a carboxylic acid having about 1 to about 4 carbon atoms or a combination solvent of methanol and a carboxylic acid. A carboxylic acid having at least about 10 carbon atoms can be then added to the cement of the neutralized sulfonated polymer thereby forming a barium salt of the carboxylic acid having at least about 10 carbon atoms in situ, wherein the barium salt of the carboxylic acid having at least about 10 carbon atoms is a preferential plasticizer for the zinc sulfonate groups. The Brookfield viscosity at 3.0 rpm at room temperature of the cement of the barium neutralized sulfonated polymer is less than about 50,000 cps.
2. Description of the Prior Art
Recently, a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728, herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized on a two-roll mill with a basic material to form an ionically crosslinked elastomer at room temperature having substantially improved physical properties over an unsulfonated elastomer. These sulfonated elastomers, may be processed somewhat like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer.
The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from the group consisting of Groups I, II, III, IV, V, VIB, VIIB and VIII and mixtures thereof of the Periodic Table of Elements.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the unneutralized sulfonated elastomeric polymers in solution are organic amines dissolved in an aliphatic alcohol. The resultant neutralized sulfonated elastomeric polymer prepared by this process exhibit somewhat inferior physical properties due to a rather low degree of ionic association.
U.S. Pat. Nos. 3,870,841 and 3,847,854 herein incorporated by reference, teach a method of plasticization of the polymeric backbone of a neutralized sulfonated polymer. The plasticizing agent is incorporated into the sulfonated polymer by hot melting the neutralized sulfonated polymer with the plasticizing agent. Although the rheological properties are improved, the incorporation of these plasticizing agents into the neutralized sulfonated polymers is extremely difficult and usually results in a general decrease in physical properties.
The four aforementioned patents teach the method of compounding the additives into the neutralized sulfonated elastomeric polymer under high heat and shear conditions or the use of an organic amine neutralizing agent thereby resulting in compositions either having poor rheological or physical properties.
The present invention teaches a new improved process for the formation of an improved gel-free neutralized sulfonated polymer having both excellent rheological and physical properties. The improvement in the process comprises the neutralization of the sulfonated cement by the addition of a barium type neutralizing agent dissolved in a solvent system of a carboxylic acid having about 1 to about 4 carbon atoms or a mixture of methanol and a carboxylic acid having about 1 to about 4 carbon atoms which can be followed by the subsequent addition of a carboxylic acid having at least about 10 carbon atoms to form in situ a barium salt of the carboxylic acid having at least about 10 carbon atoms which acts as a preferential plasticizer for the barium neutralized sulfonate groups.